From: Dan Carpenter <dan.carpenter@oracle.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
kernel-janitors@vger.kernel.org
Subject: [PATCH] x86/ldt: Off by one in get_segment_base()
Date: Fri, 18 Aug 2017 10:30:30 +0000 [thread overview]
Message-ID: <20170818102516.gqwm4xdvvuvjw5ho@mwanda> (raw)
ldt->entries[] is allocated in alloc_ldt_struct(). It has
ldt->nr_entries elements and ldt->nr_entries is capped at LDT_ENTRIES.
So if "idx" is = ldt->nr_entries then we're reading beyond the end of
the buffer. It seems duplicative to have two limit checks when one
would work just as well so I removed the check against LDT_ENTRIES.
The gdt_page.gdt[] array has GDT_ENTRIES entries.
Fixes: d07bdfd322d3 ("perf/x86: Fix USER/KERNEL tagging of samples properly")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
---
This is a static checker fix. I'm pretty certain it's correct. But I
don't understand the code terribly well, so please let me know and I'll
be happy to send a v2 if needed.
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index af12e294caed..939050169d12 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2335,12 +2335,9 @@ static unsigned long get_segment_base(unsigned int segment)
#ifdef CONFIG_MODIFY_LDT_SYSCALL
struct ldt_struct *ldt;
- if (idx > LDT_ENTRIES)
- return 0;
-
/* IRQs are off, so this synchronizes with smp_store_release */
ldt = lockless_dereference(current->active_mm->context.ldt);
- if (!ldt || idx > ldt->nr_entries)
+ if (!ldt || idx >= ldt->nr_entries)
return 0;
desc = &ldt->entries[idx];
@@ -2348,7 +2345,7 @@ static unsigned long get_segment_base(unsigned int segment)
return 0;
#endif
} else {
- if (idx > GDT_ENTRIES)
+ if (idx >= GDT_ENTRIES)
return 0;
desc = raw_cpu_ptr(gdt_page.gdt) + idx;
reply other threads:[~2017-08-18 10:30 UTC|newest]
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